AAPT2: Differentiate between Android and Java package names

Android package names are more strict (ASCII only) than Java package names.
Also fixed an issue where trailing underscores were disallowed in Android
package names.

Bug: 68468089
Test: make aapt2_tests
Merged-In: I1052e9e82b6617db6065ce448d9bf7972bb68d59
Change-Id: I1052e9e82b6617db6065ce448d9bf7972bb68d59